The present invention relates to a fuser roller. More particularly, this invention relates to a polyperfluoroalkoxy (PFA) sleeved fuser roller for producing good fusing and high image quality in electrophotographic imaging and recording processes.
In imaging methods, such as electrostatographic imaging, and recording processes, such as electrophotographic copying, an electrostatic latent image formed on a photoconductive surface is developed with a thermoplastic toner powder. The thermoplastic toner powder is then fused to a receiver to create an image. The fusing member can be a roll, belt, or any surface having a suitable shape for fixing the thermoplastic toner powder to the receiver. The fusing step commonly consists of passing the receiver, for example, a sheet of paper, on which toner powder is distributed in the form of an image, through the nip of a pair of rolls. At least one of the rolls is heated. In the case where the fuser member is a heated roll, a smooth resilient surface is bonded either directly or indirectly to the core of the roll.
A toner fuser roll includes a cylindrical core, often metallic, that typically has a heating source in its interior. A resilient base cushioning layer, which may contain filler particles to improve mechanical strength and/or thermal conductivity, is formed on the surface of the core, which may advantageously be coated with a primer to improve adhesion of the resilient layer. Roller cushioning layers are commonly made of silicone rubbers or silicone polymers such as, for example, poly(dimethylsiloxane) polymers (PDMS) of low surface energy, which minimize adherence of toner to the roller. Frequently, release oils composed of, for example, poly(dimethylsiloxanes) are also applied to the fuser roll surface to prevent the toner from adhering to the roll. Such release oils may interact with the PDMS in the resilient layer upon repeated use, which in time causes swelling, softening, and degradation of the roll.
In previous technologies, such as U.S. Pat. No. 6,224,978 (incorporated herein by reference), a fuser roller includes three concentric layers each containing particulate fillers. These three layers include a base cushioning layer containing a condensation-cured PDMS, a barrier layer covering the base cushioning and containing a cured fluorocarbon polymer, and an outer surface layer containing an addition-cured PDMS. The particulate fillers in each layer include one or more of aluminum oxide, iron oxide, calcium oxide, magnesium oxide, tin oxide, and zinc oxide. The barrier layer, which may be a Viton™ elastomer (sold by DuPont) or a Fluorel™ elastomer (sold by Minnesota Mining and Manufacturing), is a relatively low modulus material typically having a Young's modulus less than about 10 MPa. Therefore, it has a negligible effect upon the mechanical characteristics of the roller, including the overdrive. Although the barrier layer prevents swelling of the roller, the silicone surface is subject to excessive wear and abrasion.
Fluoroelastomer surface coatings for fuser rollers are also mentioned, for example, in U.S. Pat. Nos. 5,595,823 and 5,851,673, (both incorporated herein by reference). Fluoroelastomers have improved wear resistance compared to silicones but are generally not as chemically resistant. The fluoroelastomer is subject to staining by toner components leading to degradation of the material and toner offset.
Fluoroplastic sleeves offer the advantage of excellent wear resistance as well as excellent chemical resistance. Unfortunately, plastic sleeves are generally of very high hardness and actually perform poorly in some applications due to poor conformability with the receiver surface. Poor conformability to the receiver surface also produces poor image quality. Having a soft cushion provides better fusing properties; however, it also stretches the sleeve and causes wrinkles in the sleeve. Moreover, thin or soft sleeves are also preferred for improved fusing properties, but these are also more prone to wrinkling. A thicker sleeve may avoid wrinkling, but it also reduces fusing quality as well as image quality. Elastomeric coatings such as fluoroelastomer coatings do not suffer wrinkling as readily from stretching as they have much greater extensability than plastic coatings including sleeves.
Accordingly, there is a need to provide a sleeved fuser member that avoids wrinkling but does not suffer reduced fusing quality. More specifically, it would be desirable to provide a cushioned fuser member with a thin plastic sleeve that does not suffer from wrinkling. In particular it would be desirable to provide a sleeved cushioned fuser roller in an externally heated fuser system that has good fusing performance and does not suffer from wrinkling.